DIETARY EFFECTS ON PREDICTION OF BODY MASS CHANGES IN BIRDS BY PLASMA METABOLITES

Concentrations of plasma metabolites, including triglyceride, glycerol, and B-OH butyrate, can be used to determine refueling performance of migratory birds. We tested the effects of diet type and diet lipid content on the predictive relationships between metabolites and body mass changes in three species of passerines in captivity. In addition, we tested whether measurement of plasma phospholipids improved predictions of mass change. Rate of mass change was positively related to triglycerides in a captive frugivore (Cedar Waxwing; Bombycilla cedrorum) and a granivore (White-crowned Sparrow; Zonotrichia leucophrys). B-OH butyrate was negatively and nonlinearly related to mass change in Cedar Waxwings and White-crowned Sparrows. Glycerol was negatively related to mass change in Cedar Waxwings but not in White-crowned Sparrows. Mass change was positively related to triglycerides and negatively related to B-OH butyrate in Yellow-rumped Warblers (Dendroica coronata). There was no effect of diet lipid content (9% vs. 28% dry mass) on these predictive relationships. Plasma phospholipids were positively related to mass change in White-crowned Sparrows, but negatively related to mass change in Yellow-rumped Warblers and not related to mass change in Cedar Waxwings. Measurement of phospholipids did not improve prediction of mass change by metabolite profiles. Nevertheless, plasma metabolite profiles are predictive of short- term mass changes in captive birds regardless of diet type or diet lipid content, and can provide valuable information on refueling performance in studies of stopover ecology. Efectos de la Dieta sobre las Predicciones de los Cambios en el Peso Corporal de Aves por medio de Metabolitos Plasmáticos